1. Field of the Invention
The present invention pertains to fluid infusion apparatus for administering injectable liquid in a controlled manner to a patient, and more particularly, it pertains to fluid infusion devices of the portable type which are adapted to be used with ambulatory patients and outside of the normal hospital environment.
2. Description of the Prior Art
Infusion apparatus for injecting medications or life sustaining fluids intervenously into a patient have been in general use for many years in hospitals as is well known. Increasingly, such devices of a portable variety have been used where the patient is ambulatory. Thus, with a portable infusion device the patient may walk about the hospital grounds or the device may be used while the patient is at home or at work.
Generally speaking, portable infusion devices may be fairly small and compact so they can be carried by the patient without any obvious difficulties and so that he will not be seriously inconvenienced. Yet, such devices must be foolproof and capable of sustained accurate operation in any physical orientation and while the patient is rapidly moving about.
Portable infusion devices on the market today generally comprise two different types. One type uses a positive displacement pump or other conventional pump which automatically pumps small amounts of fluid from a reservoir into the patient on a predetermined schedule. The other type of device utilizes the more or less standard syringe and operates to drive the plunger of the syringe in a continuous or controlled intermittent manner, typically by the use of a lead screw or rack and pinion mechanism.
The U.S. patent to Szabo et al U.S. Pat. No. 3,886,938 discloses a portable fluid infusion device utilizing a standard syringe with a rack and pinion mechanism driving the plunger of such syringe through an appropriately controlled timing mechanism. Other rack and pinion drives for portable fluid injecting syringes can be found in the prior U.S. patents to Becker U.S. Pat. No. 4,231,368 and Smith U.S. Pat. No. 1,718,596--both of which disclose devices of the "hand gun" design.
A relatively compact portable infusion apparatus is disclosed in the U.S. patent to Hessberg et al U.S. Pat. No. 4,300,554 wherein a syringe is operated through a rack and pinion mechanism which is mounted in a closely spaced parallel arrangement with the syringe.
In yet another prior art portable infusion device, as disclosed in the U.S. patent to Babb et al U.S. Pat. No. 4,313,439, the plunger of a syringe is connected to a driving mechanism (either a compressed spring or a rack and pinion device) through a series of balls arranged in a U-shaped guide track so that the driving mechanism lies in parallel with the syringe and its plunger.
In all of the aforedescribed devices of the prior art, which utilize more or less standard fluid-injecting syringes, the apparatus must be made long enough in the dimension parallel to the body of the syringe so as to accomodate not only the syringe but also the full length of the plunger stem when the plunger is fully retracted in the syringe body.